1. Field of the Invention
The present invention relates to a mobile communication network system, a foreign agent router, an address server and a packet delivery method employed therein. More particularly, the invention relates to a network system consisted of fixed IP (Internet Protocol) subnetworks.
2. Description of Related Art
Conventionally, in a network system consisted of fixed IP subnetworks of this kind, when mobile IP [Mobile IP (ver. 4)] is made use of, there are following two kinds of arrangement configuration as arrangement configuration of home agents performing position management of IP terminal (mobile nodes).
The first arrangement configuration is a configuration frequently used in a local area network (LAN) or the like. In this configuration, a mobile IP compatible router is arranged in a desktop LAN, such as Ethernet (trademark) or the like. The router serves as a home agent including IP terminals belonging in the subnetworks and as a foreign agent for external IP terminals roaming to the subnetwork.
The second arrangement configuration is a configuration to adapt a virtual subnetwork, namely a subnetwork actually having no belonging terminal to deal a mobile IP terminal as moving outside irrespective of the position thereof so that the home agent transmits packets to the subnetwork where the mobile IP terminal is present. In this case, the home agent may be arranged anywhere. However, it is efficient to arrange the home agent in the vicinity of a gateway connected to external network.
In this case, in the second arrangement configuration, as shown in FIG. 6, when the mobile IP terminal [mobile node (MN)] 13 connected to the home agent (HA) 11 through a home link 101 moves to be connected to the foreign agent (FA) 12 via an external link 102, the home agent 11 transfers the packet from a communication counterpart (CN) 14 to the mobile IP terminal 13, to the foreign agent 12 for delivery to the mobile IP terminal 13 from the foreign agent 12.
Here, Mobile IP (ver. 4) has been described in RFC (Request for Comments) 2002 of IETF (Internet Engineering Task Force), C. Perkins (IBM), Editor, October 1996.
Basic operation of this Mobile IP (ver. 4) will be discussed hereinafter. The mobile IP terminal 13 performs agent discovery as in which of the home link 101 or the external link 102, it is included by receiving the public notice of the Agent. When the mobile IP terminal 13 makes agent discovery as being included in the home link 101, mobility service is not used.
When the mobile IP terminal 13 makes agent discovery as being included in the external link 102, an address of the foreign agent 12 or an address (co-located: second address) obtained from DHCP (Dynamic Host Configuration Protocol) is registered to the own home agent 11 as care of address. At this time, the mobile IP terminal 13 may register the care of address to the home agent 11 via the foreign agent 12. On the other hand, the mobile IP terminal 13 updates position registration to the home agent 11 upon returning from the external link 102 to the home link 101.
The packet from the communication counterpart 14 to the mobile IP terminal 13 is captured by the home agent 11, is transferred using tunnel to the care of address and is delivered to the mobile IP terminal 13 based on the care of address. The packet from the mobile IP terminal 13 to the communication counterpart 14 is basically transported by a general IP packet transporting mechanism (e.g. IP router network 100).
It has also been proposed an option of a route optimizing function performing route optimization between the communication counterpart 14 and the mobile IP terminal 13 by notifying presenting zone position (care of address) of the mobile IP terminal 13 to the communication counterpart 14 in transfer of packet from the communication counterpart 14 to the mobile IP terminal 13. It should be noted that in Mobile IP (ver. 6), as shown in FIG. 7, study has been made not as optional transfer method.
In the conventional network system set forth above, when the former transfer method via the home agent is selected, concentration of traffic to the home agent can be caused to significantly restrict throughput of the entire network system.
On the other hand, when the option using the later route optimizing function is selected, while concentration of traffic to the home agent can be avoided, since the presenting zone position of the mobile IP terminal is notified to the communication counterpart, demand for privacy protection to hide the presenting zone position of the mobile IP terminal cannot be satisfied.